This sequel adds new enemy ships to the alien fleet such as firebombers, Yllabian Space Guppies (note that Yllabian is based on "Yllab", the word "Bally" spelled backwards, a friendly poke at Williams' then-competitor, Bally-Midway), Dynamos and Space Hums. The Defender ship is now equipped with an Inviso cloaking device, which renders the ship invulnerable when activated, but has a limited charge. A Stargate will transport the ship to any humanoid in trouble. There are now two special stages, the Firebomber Showdown and the Yllabian Dogfight, that occur every fifth and tenth wave.